The present invention relates to attachment arrangements for attaching battery packs to cordless electric devices. More particularly, the present invention relates to a twist lock attachment arrangement for a battery pack.
Battery packs for powering cordless electric devices, such as portable drills, impact wrenches and the like, are well known. It has been found convenient to have the battery packs releasably mounted in the cordless devices, such as in or connected to the handle portions thereof, with a quick release type of latching arrangement so that the battery packs can be easily removed for recharging.
Generally, two types of battery pack attachment arrangements have been utilized, namely, a “stem pack” design and a “slide pack” design. With reference to FIG. 1, an illustrative stem pack design is shown. The illustrative electric tool 10 includes a head 12, a tool holder 14, a motor (not shown), a hollow handle 16 and a switch 18. The hollow handle 16 depends from the head 12 and may be formed integrally therewith or as separate component attached thereto. In either construction, the handle 16 is generally formed as two halves 17A and 17B which are interconnected via screws or the like (not shown). An electric circuit and wiring (not shown) are housed in the hollow handle 16.
The battery pack 20 is configured to connect to the hollow handle 16 and provide power to the electric tool 10. The battery pack 20 has a top surface 22 with an extended portion 24 configured to be received in the hollow handle 16. The extended portion 24 typically houses on or more battery cells therein such that the battery pack 20 external portion can be made smaller and the hollow space within the handle 16 is utilized, rather than being a dead space. The upper end of the extended portion 24 has one or more contacts 26 configured to contact internal contacts (not shown) within the electric tool 10. Since the extended portion 24 extends into the hollow handle 16, the internal contacts can be provided within the hollow handle 16 spaced from the opening into the hollow handle 16, thereby protecting the internal contacts.
The attachment arrangement for the battery pack 20 includes one or more biased latches 28. Each latch 28 is configured to engage a shoulder or the like (not shown) within the hollow handle 16. To attach the battery pack 20 to the electric tool 10, the extended portion 24 of the battery pack 20 is linearly inserted into the hollow handle 16 until the latches 28 snap into engagement with the respective shoulders within the hollow handle 16. To remove the battery pack 20, a push button 30 is associated with each latch 28. Depression of the push button 30 disengages the latch 28 from the respective shoulder.
When the battery pack 20 is connected with the electric tool 10, the latches 28 are directly burdened with the whole weight of the battery pack 20. Over time, the continuous load on the latches 28 and respective shoulders causes the latches 28 to wear out and may also cause the handle halves 17A and 17B to spread apart, which results in the battery pack 20 being less securely connected. As a result, the battery pack 20 may have a less reliable electrical connection or may be subject to inadvertent disconnection from the tool 10. Additionally, even if the latches 28 have not worn, the battery pack 20 may still be subject to inadvertent disconnection if the push buttons 30 are inadvertently depressed.
Referring to FIGS. 2 and 3, an illustrative slide pack design is shown. The electric tool 10′ again includes a hollow handle 16′. With the slide pack design, the internal contact 15 is provided adjacent to the end of the handle 16′ to facilitate contact with the battery pack contact 26′, as described hereinafter. As can be seen in FIG. 2, most of the hollow space within the hollow handle 16′ is unused, dead space.
The attachment arrangement for the battery pack 20′ includes rails 32 on opposed sides of the battery pack 20′ which define opposed slots 34. The slots 34 are configured to receive rails 19 provided on opposed sides of the tool handle 16′. To attach the battery pack 20′ to the tool 10′, the battery pack 20′ is slid transversely to the axis of the handle 16′, as indicated by arrow A in FIG. 2, such that the rails 19 are received in the slots 34. A releasable snap latch 33 or the like is provided on the battery pack 20′ to secure the battery pack 20′ to the tool 10′ and prevent axial movement thereof. The weight of the battery pack 20′ is supported by the rails 19 and slots 34. The latch 33 is not burdened with the weight of the pack 20′, but instead only needs to prevent axial movement. While this design is advantages with respect to weight support, the transverse sliding of the battery pack 20′ relative to the tool handle 16′ prevents extension of the battery pack 20′ beyond the upper rail 32. As a result, the space within the hollow handle 16′ is not utilized and the battery pack 20′ must have a larger external configuration to house an equal number of battery cells as the stem design. Additionally, the battery pack contact 26′ also must be provided within the confines of the battery pack 20′, thereby requiring the tool internal contact 15 to be provided at an exposed position at the end of the handle 16′.